Mechanical and chemical-mechanical planarizing processes (collectively "CMP") are used in the manufacturing of microelectronic devices for forming flat surfaces on semiconductor wafers, field emission displays and other types of microelectronic-device substrate assemblies. FIG. 1 schematically illustrates a portion of an existing planarizing machine 10 having a rotating platen 20, a carrier assembly 30 and a polishing pad 50. An under-pad 25 can be attached to an upper surface 22 of the platen 20 for supporting the polishing pad 50. In many planarizing machines, a drive assembly 26 rotates (arrow A) and/or reciprocates (arrow B) the platen 20 to move the polishing pad 50 during planarization. In other planarizing machines, such as web-format planarizing machines, the platen 20 remains stationary during planarization and the carrier assembly 30 moves a substrate assembly 12 across the polishing pad 50.
The carrier assembly 30 controls and protects the substrate assembly 12 during planarization. The carrier assembly 30 typically has a drive assembly, a driveshaft 31 coupled to the drive assembly, and a carrier head 33 coupled to the driveshaft 31. The drive assembly typically rotates and/or translates the carrier head 33 to move the substrate assembly 12 across the polishing pad 50 in a linear, orbital and/or rotational motion.
The particular carrier head 33 illustrated in FIG. 1 is manufactured by Applied Materials Corporation. This carrier head includes an external housing 34, a backing plate 40 fixedly attached to the driveshaft 31, and a bladder 46 attached to the backing plate 40. The housing 34 has a support member 35 and a retaining ring 37 depending from the support member 35. A smooth-walled portion of the driveshaft 31 is received in a hole 36 through the support member 35 so that the driveshaft 31 can rotate independently from the housing 34.
The backing plate 40 of the carrier head 33 includes an annular rim 41 having an inner surface 42 extending around the perimeter of the rim 41. The inner surface 42 is a straight, vertical wall extending upwardly from the rim 41. The backing plate 40 also includes a disposable pad 43 adhered to the annular rim 41. The disposable pad 43 is shaped to have a flat interior portion 44 and a curved perimeter portion 45 curving from the interior portion 44 to the rim 41. The pad 43 is a thin, low-friction sheet separate from the backing plate 40 that prevents the bladder 46 from sticking to the backing plate 40 during planarization. The backing plate 40 is received in the housing 34, and a number of inner tubes 49a and 49b support the housing 34 over the backing plate 40. The backing plate 40 accordingly rotates directly with drive shaft 31 without necessarily rotating with or moving vertically with the housing 34.
The bladder 46 is a thin, flexible membrane attached to the backside or the perimeter edge of the backing plate 40. A fluid conduit 47 through the driveshaft 31, the backing plate 40 and the pad 43 couples a fluid supply (not shown) with a cell 48 between the bladder 46 and the pad 43. The fluid supply can drive fluid into the cell 48 to inflate the bladder 46, or the fluid supply can withdraw fluid from the cell 48 to deflate the bladder 46.
To planarize the substrate assembly 12, the carrier head 33 retains the substrate assembly 12 on a planarizing surface 52 of the polishing pad 50 in the presence of a planarizing fluid 60. The bladder 46 inflates to exert a desired downforce against the substrate assembly 12, and the carrier head 33 moves and/or rotates the substrate assembly 12. As the substrate assembly 12 moves across the planarizing surface 52, abrasive particles and/or chemicals in either the polishing pad 50 or the planarizing solution 60 remove material from the surface of the substrate assembly 12.
CMP processes must consistently and accurately produce a uniformly planar surface on the substrate assembly to enable precise fabrication of circuits and photo-patterns. One aspect of forming components on semiconductor or other microelectronic-device substrate assemblies is photo-patterning designs to within tolerances as small as approximately 0.1 .mu.m. Many semiconductor fabrication processes, however, create highly topographic surfaces with large "step heights" that significantly increase the difficulty of forming sub-micron features or photo-patterns to within such small tolerances. Thus, CMP processes are often used to transform a topographical substrate surface into a highly uniform, planar substrate surface (e.g., a "blanket surface").
In the competitive semiconductor industry, it is also desirable to maximize the throughput of CMP processing by producing a blanket substrate surface as quickly as possible without sacrificing the accuracy of the process. The throughput of CMP processing is a function of several factors, one of which is the ability to accurately form a flat, planar surface across as much surface area on the substrate assembly as possible. Another factor influencing the throughput of CMP processing is the ability to stop planarization at a desired endpoint in the substrate assembly. In a typical CMP process, the desired endpoint is reached when the surface of the substrate is a blanket surface and/or when enough material has been removed from the substrate assembly to form discrete components on the substrate assembly (e.g., shallow trench isolation areas, contacts, damascene lines, etc.). Accurately stopping CMP processing at a desired endpoint is important for maintaining a high throughput because an "under-planarized substrate assembly may need to be re-polished, or an "over-planarized" substrate assembly may be damaged. Thus, CMP processing should be consistent from one wafer to another to accurately form a blanket surface at the desired endpoint.
One drawback of the Applied Materials carrier head 33 shown in FIG. 1 is that the low-friction pad 43 wears out and needs to be replaced. In a typical application, for example, vertical displacement of the substrate assembly 12 and the backing plate 40 causes the bladder 46 to periodically engage the perimeter of the pad 43. The contact between the bladder 46 and the pad 43 wears down the perimeter surface of the pad 43 to a point at which the pad 43 must be replaced. Replacing the pad 43, however, is time-consuming because the bladder 46 and the pad 43 must be removed from the backing plate 40. Therefore, the Applied Materials carrier head 33 illustrated in FIG. 1 is subject to downtime that reduces the throughput of CMP processing.
Another drawback of the carrier head 33 is that it may produce inconsistent, non-planar surface features at the edge of a substrate assembly. The planarity of the substrate assembly is a function of, at least in part, the pressure exerted on the substrate assembly by the bladder 46. The contour of the perimeter region 45 of the low-friction pad 43 may affect the force exerted on the perimeter of the substrate assembly 12. For example, because the substrate assembly 12 may press the bladder 46 against the perimeter region 45 of the pad 43 during planarization, the contour of the perimeter region 45 can directly affect the force exerted against the perimeter of the substrate assembly 12. The shape of the perimeter region 45 of the pad 43, however, may be inconsistent over the life of a single pad 43 or from one pad 43 to another. One reason that the shape of the pad 43 may change is because the perimeter region 45 of the pad 43 compresses after a period of use. Moreover, and even more problematic, the shape of the perimeter region 45 may be different from one pad 43 to another because each pad 43 is manually attached to the backing plate 40. Therefore, the inconsistencies of the pad 43 may produce inconsistent, non-planar surface features at the edge of the substrate assemblies.